There is no puffer that can be considered truly safe in a community tank, as each puffer has their own personality, even with the "gentle" MBU, you could end up getting one thats an absolute killer...
The only one that would be considered some what safe with other fish, besides the MBU which requires a huge tank to match, is the South American Puffer (which is a schooling puffer), although these stay pretty small at about 6" if i'm not mistaken (too lazy to double check) and require a lot of teeth trimming...
As for fastest growing, i guess its probably between the fahaka and MBU, i know my fahaka for the first year grew on average at least 1" - 1.5" a month to the point where she is now about 13" - 14" although shes slowed down a lot now...
Hope that helps a little...